Lanthanide oxide/zirconium oxide atomic layer deposited nanolaminate gate dielectrics

ABSTRACT

The invention provides a laminated dielectric layer for semiconductor devices formed by a combination of ZrO 2  and a lanthanide oxide on a semiconductor substrate and methods of making the same. In certain methods, the ZrO 2  is deposited by multiple cycles of reaction sequence atomic layer deposition (RS-ALD) that includes depositing a ZrI 4  precursor onto the surface of the substrate in a first pulse followed by exposure to H 2 O/H 2 O 2  in a second pulse, thereby forming a thin ZrO 2  layer on the surface. After depositing the ZrO 2  layer, the lanthanide oxide layer is deposited by electron beam evaporation. The composite laminate zirconium oxide/lanthanide oxide dielectric layer has a relatively high dielectric constant and can be formed in layers of nanometer dimensions. It is useful for a variety of semiconductor applications, particularly for DRAM gate dielectric layers and DRAM capacitors.

TECHNICAL FIELD

The invention relates to the field of semiconductor dielectric layers,and particularly to dielectric layers used in the formation oftransistor gates and capacitors in dynamic random access memory devices.

BACKGROUND OF THE INVENTION

Dynamic Random Access Memory Devices (DRAMs) have become the standardtype of storage device in modern computer systems. Modern DRAMs are highdensity, highly integrated structures having a variety ofconfigurations, most typically stacked and trench configurations. Asever increasing density is sought, more sophisticated manufacturingprocesses and materials are required to achieve sub micron sizedelectrical component layers with reliable conformity to operationalspecifications.

As density increases, the minimum feature sizes of DRAM componentsapproach 100 nm and smaller. For example, the gate dielectric materialthickness of MOS devices may be required to be 20 nm (200 Å) or less incertain designs. In this thickness range the most commonly used gatedielectrics, SiO₂, is not suitable because of leakage current caused bydirect tunneling. As a result, gate dielectric materials with highdielectric constants (k) and large band gap with a favorable bandalignment, low interface density, and good thermal stability are neededfor future gate dielectric applications.

There are many known high-k unilaminate dielectric materials with highdielectric constants, such as Ta₂O₅, TiO₂ and SrTiO₃, but unfortunatelythese materials are not thermally stable when formed directly in contactwith silicon. In addition, the interface of such materials need to becoated with a diffusion barrier, which not only adds process complexity,but also defeats the purpose of using the high-k dielectric. This addedinterfacial layer becomes a series capacitor to the gate capacitance,and degrades the high capacitance. Moreover, materials having too highor too low a dielectric constant may not be an adequate choice foralternate gate applications. Ultra high-k materials such as SrTiO₃ maycause fringing-field induced barrier lowering effect. On the other hand,materials with relatively low dielectric constant such as Al₂O₃ and Y₂O₃do not provide sufficient advantage over the SiO₂ or Si₃N₄.

Lanthanide oxides have also been investigated as possible dielectricmaterials for use in gate dielectric oxides. Jeon et al reported aninvestigation of the electrical characteristics of amorphous lanthanideoxides prepared by electron beam evaporation and sputtering (Jeon etal., Technical Digest of Int'l Electron Devices Meetings, 471-474,2001). Excellent electrical characteristics were found for the amorphouslanthanide oxides including a high oxide capacitance, low leakagecurrent, and high thermal stability. Typical dielectric constants rangedbetween 11.4 and 15.0 in thin samples. Accordingly, lanthanide oxidesalone may be a suitable alternative for certain applications usingsingle layers of dielectric material. Also, a single layer of ZrO₂ maybe used in certain applications. Recently, a zirconium oxide layerformed by atomic layer deposition (ALD) from an iodide precursor wasshown to have exhibit a relative permititivity at 10 kHz of about 23-24for films deposited at 275-325° C. (Kukli et al, Thin Solid Films 410,53-56 (2003)).

An alternative configuration for gate electrode dielectric layers is acomposite laminate dielectric layer made of two or more layers ofdifferent materials. Thin (about 10 nm) nanolaminate dielectricmaterials made of layers of tantalum oxide and hafnium oxide(Ta₂O5-HfO₂), tantalum oxide and zirconium oxide (Ta₂O₅—ZrO₂) orzirconium oxide hafnium oxide (ZrO₂—HfO₂) deposited on a siliconsubstrate by ALD were characterized for possible gate dielectricapplications by Zhang et al, J. App. Physics, 87 (4) 1921-1924 (2000).The dielectric constants of these films were in the range of 12-14 andthe leakage currents were in the range of 2.6×10⁻⁸ to 4.2×10⁻⁷ A/cm⁻² atMV/cm electric field.

The ALD method of forming layers is also known as “alternately pulsedchemical vapor deposition.” ALD was developed as a modification ofconventional CVD techniques. While there are a variety of variations onALD, the most commonly used method is reaction sequence ALD (RS-ALD). InRS-ALD, gaseous precursors are introduced one at a time to the substratesurface in separate pulses. Between pulses, the reactor is purged withan inert gas or is evacuated. In the first reaction step, the precursoris saturatively chemi-adsorbed at the substrate surface, and during thesubsequent purging step, free precursor is removed from the reactor. Inthe second step, another precursor is introduced on the substrate andthe desired film growth reaction takes place on the substrate surface.When the chemistry is favorable, the precursors adsorb and react witheach other aggressively forming the film. Subsequent to film growth, theby-products and excess precursors are finally purged from the reactor.One advantage of RS-ALD is that one cycle of first precursor depositing,purging, second precursor depositing, reaction, and final purging can beperformed in less than one second in a properly designed flow typereactor.

One striking feature of RS-ALD is the saturation of all the reaction andpurging steps, which makes the growth self-limiting. This allows forlarge area uniformity and conformality to planar substrates and deeptrenches, even in the extreme cases of porous silicon or high surfacearea silica and alumina powders. The control of film thickness isstraight forward and can be made by simply calculating the growthcycles. ALD was originally developed to manufacture luminescent anddielectric films needed for electroluminescent displays where mucheffort was put to the growth of doped zinc sulfide an alkaline earthmetal sulfide films. Later ALD was studied for the growth of differentepitaxial composite II-V, and II-VI films, nonepitaxial crystalline oramorphous oxide and nitride firms in composite multiplaner structures.Unfortunately however, although considerable effort was put into use ofALD for growth of silicon and germanium films, difficult precursorchemistry precluded success in this area.

There is therefore a need in the art to provide other types of compositelaminate dielectric layers, particularly using the favorable features ofRS-ALD deposition methods.

SUMMARY OF THE INVENTION

The present invention provides semiconductor devices that include asubstrate material and a composite laminate dielectric layer formed onthe substrate material. The composite laminate dielectric layer includesa layer of ZrO₂ and a layer of a lanthanide oxide formed on the ZrO₂layer. Alternatively, the composite laminate dielectric layer includesthe layer of ZrO₂ formed on the layer of lanthanide oxide. In generalembodiments, the lanthanide oxide layer may be made of any one of Pr₂O₃,Nd₂O₃, Sm₂O₃, Gd₂O₃, Dy₂O₃ and PrTixOy, where x and y are variable,typically in a ratio of 1.0 x to 0.9-1.0 y.

In certain embodiments, the composite laminate dielectric layer is agate dielectric layer of a MOS transistor. In other embodiments, thecomposite laminate dielectric layer is a dielectric insulating layer ofa semiconductor capacitor. Other embodiments include MOS gate dielectriclayers, semiconductor capacitors and DRAMs having one or more of thecomposite laminate dielectric layers made of the ZrO₂ layer and thelanthanide oxide layer. In certain embodiments for a transistor gateelectrode dielectric, the ZrO₂ layer has a thickness of between about 1to about 6 nm and the lanthanide oxide layer has a thickness of about 2to 12 nm. In various embodiments, the ZrO₂ layer is formed on asubstrate by RS-ALD from a ZrI₄ precursor and an oxygen precursor,typically H₂O/H₂O₂, and the lanthanide oxide layer is formed by electronbeam evaporation of a lanthanide oxide.

In another aspect, the invention includes methods of forming a compositelaminate dielectric layer for a semiconductor device, that includes thesteps of depositing a layer of ZrO₂ on a silicon substrate anddepositing a layer of lanthanide oxide on the ZrO₂ layer or vice versa.In one embodiment, the ZrO₂ oxide layer is formed by RS-ALD from a ZrI₄precursor. In another embodiment, the lanthanide oxide layer is formedby electron beam evaporation of a lanthanide oxide. In still anotherembodiment, the ZrO₂ layer is formed RS-ALD of ZrI₄ H₂O/H₂O₂ precursors,and the lanthanide oxide layer is formed by electron beam evaporation ofa lanthanide oxide.

Another aspect of the invention is a system for forming the foregoingcomposite laminate dielectric layers on a substrate. The system includesa first reaction vessel configured for depositing a layer of ZrO₂ on asilicon substrate and a second reaction vessel configured for depositinga layer of lanthanide oxide on the ZrO₂ layer. In certain embodiments,the first reaction vessel is configured for depositing the ZrO₂ layer byRS-ALD and the second reaction vessel is configured for depositing thelanthanide oxide layer by electron beam evaporation. The system alsoincludes means for transporting the substrate between the first and thesecond reaction vessels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional drawing of a general embodiment ofsemiconductor device having a composite laminate dielectric layeraccording to one embodiment of the invention.

FIG. 2 is a partial cross-sectional drawing of a general embodiment of aMOS transistor having the composite laminate dielectric layer accordingto another embodiment of the invention.

FIG. 3 is a partial cross-sectional drawing of a general embodiment ofsemiconductor capacitor transistor having the composite laminatedielectric layer according to another embodiment of the invention.

FIGS. 4A and 4B are partial cross-sectional drawings of exemplaryembodiments of memory cells, having one or more composite laminatedielectric layers according to another embodiment of the invention.

FIG. 5 illustrates an e-beam evaporation vessel for forming at least oneof the lanthanide oxide layer or ZrO₂ layers that form the transistorthe laminate dielectric layer according to another embodiment of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In setting forth the invention in detail, citation is made to variousreferences that may aid one of ordinary skill in the art in theunderstanding or practice of various embodiments of the invention. Eachsuch reference is incorporated herein by reference in its entirety,including the references that may be cited in the incorporatedreferences to the extent they may required to practice the invention toits fullest scope. The drawings provided herein are not to scale nor dothey necessarily depict actual geometries of the devices of theinvention. Rather, the drawings are schematics that illustrate variousfeatures of the invention in a manner readily understood by one ofordinary skill in the art, who can make actual devices based on thesedrawings and the description that follows.

FIG. 1 depicts a general embodiment of the invention, which includes asemiconductor device 10 that includes a composite laminate dielectriclayer 12 made of a ZrO₂ first layer 14 laminated to a lanthanide oxidesecond layer 16. The lanthanide oxide layer 16 may be made of anylanthanide oxide, for example, Pr₂O₃, Nd₂O₃, Sm₂O₃, Gd₂O₃, Dy₂O₃ orPrTixOy or ZrO₂. As used herein, the term “laminated” means the firstand second layers each have a surface in physical contact with oneanother. Typically the ZrO₂ layer 14 and lanthanide oxide layer 16 areannealed, alloyed or otherwise physically bonded to one another at theinterface 11 of the layers by deposition techniques. In variousembodiments, the thickness of the composite laminate dielectric layercombining both the ZrO₂ layer 14 and the lanthanide oxide layer 16 isless than 1000 nm, less than 500 nm, less than 100 nm, less than 50 nm,less than 20 nm, less than 10 nm, or less than 5 nm. Because thecomposite laminate dielectric layer 12 has nanometer dimensions, it maybe referred to as a nanolaminate dielectric material.

Typically, the composite laminate dielectric layer 12 is positionedbetween a first conductive layer 18 and a second conductive layer 20 ofthe semiconductor device 10. The first conductive layer 18 or the secondconductive layer 20 may each be a semiconductor or a metal in certainembodiments, or one may be a semiconductor and the other may be a metalin other embodiments.

The relative thickness of the ZrO₂ layer 14 and the lanthanide oxidelayer 16 can be varied. In one embodiment, where the composite laminatedielectric layer 12 may be used for a MOS component, for example, as agate dielectric, the lanthanide oxide layer 16 may be equal in thicknessto the ZrO₂ layer 14, or alternatively, the lanthanide oxide layer 16may be up to 5 times the thickness of the ZrO₂ layer 14. In embodimentswhere the composite laminate dielectric layer 12 is used for otherdevices, the relative thickness of the ZrO₂ layer 14 and the lanthanideoxide 16 can be varied according to need. The lanthanide oxide layer 16has a dielectric constant of about 11.4-15 while the ZrO₂ material usedfor the ZrO₂ layer 14 has a dielectric constant of about 23-25. Thecomposite laminate dielectric layer 12, therefore, will have adielectric constant between about 12 and 24 depending on the relativethickness of the layers used.

One of ordinary skill in the art can readily select the relativethickness of layers to use according to need. The “equivalent oxidethickness” (EOT) measurement, sometimes simply called “oxideequivalent,” is a convenient measure of the relative capacitance of anydielectric layer of a given thickness relative to the thickness thatmight be required in any given application. The EOT of a dielectriclayer is calculated by dividing the thickness of the layer by itssilicon oxide dielectric ratio. The silicon dioxide dielectric ratio isthe dielectric constant of the subject material divided by thedielectric constant of silicon dioxide. The dielectric constant ofsilicon dioxide is about 4. Accordingly, the silicon oxide dielectricratio for ZrO₂ is about 6 (viz, 5.75-6.25) and for lanthanide oxide isabout 3 (viz, 2.85-3.75). Therefore, for example, a 3 nm ZrO₂ layer 14has an EOT about 0.5 nm (i.e., 3 divided by 6) while a 3 nm lanthanideoxide layer 16 has an EOT of about 1 nm. The EOT of a composite laminatedielectric layer 12 made of a 3 nm of ZrO₂ layer 14 and a 3 nmlanthanide oxide layer 16 would be the sum of the oxide equivalents foreach layer, or about 1.5 nm.

One factor to consider in selecting the relative thickness of layers touse is roughness of the ZrO₂ layer 14. The ZrO₂ layer 14 has a smooth,cubic ZrO₂ crystalline structure (c-ZrO₂) within the first 5 nm whendeposited by RS-ALD as describe hereafter. This smooth structuretransitions to a more rough, tetragonal crystalline structure (t-ZrO₂)as the layer is made thicker. Accordingly, in high density embodiments,such as in MOS gate dielectric layers where a relatively smooth ZrO2layer is desirable, the ZrO₂ layer 14 should be less than about 5 nm inthickness. In capacitor applications where the smoothness of the ZrO₂layer is less critical, the ZrO₂ layer 14 can be made thicker than thelanthanide oxide layer 16 to achieve a higher dielectric constant.

As mentioned above, one embodiment of the invention is a MOS transistormade with the composite laminate dielectric layer 12 for the gatedielectric. FIG. 2 is a cross-sectional view of a general MOS transistor40 exemplifying one such embodiment of invention. The transistor 40includes conventional doped silicon semiconductor source/drain regions42 and 44, which are disposed in a substrate 46 a gate electrode 52, anda gate dielectric layer 12 a. As is well known, when a sufficientvoltage is applied to the gate electrode 52, a conductive channel region48 disposed in the substrate 46 between the source/drain regions 42 and44 is formed. The MOS transistor 40 of the invention has a gatedielectric layer 12 a made of the composite laminate dielectric layer12, which includes the ZrO₂ layer 14 and the lanthanide oxide layer 16.The thickness of the ZrO₂ layer 14 is about 1-6 nm, in variousembodiments, and typically about 3 nm or about 6 nm. The thickness ofthe lanthanide oxide layer 16 in these embodiments is about 2-12 nm. Thethickness of the composite laminate dielectric layer 12 is thereforeabout 3 to 18 nm, and more typically about 4-15 nm.

FIG. 3 is a cross-sectional view of a semiconductor capacitor 60according to another embodiment of the invention. As appreciated by oneof ordinary skill in the art, the capacitor 60 can be used in asemiconductor memory cell, for example, in a DRAM. The capacitor 60includes a conventional electrode 62, which is formed from a conductivematerial such as a metal, polysilicon or doped polysilicon. Theelectrode 62 is adjacent to one side of the composite laminatedielectric layer 12 c which is formed of the ZrO₂ layer 14 c and thelanthanide oxide layer 16 c. Another electrode 64 is adjacent to anotherside of the composite laminate dielectric layer 12 c. In a DRAM memorycell application, the electrode 64 can be coupled to an access device,such as a transistor. The thickness of the ZrO₂ layer 14 is about 1-6nm, in various embodiments, and typically about 3 nm or about 6 nm. Thethickness of the lanthanide oxide layer 16 in these embodiments is about2-12 nm. The thickness of the composite laminate dielectric layer 12 istherefore about 3 to 18 nm, and more typically about 4-15 nm.

FIGS. 4A and 4B are diagrams that depict other embodiments of theinvention, which include memory cells that contain one or more compositelaminate dielectric layers. FIGS. 4A and 4B illustrate pairs of stacked70 and trench type 71 DRAM memory cells, respectively. The DRAMS includecapacitors 60 comprised of the storage electrodes 62 and the plateelectrodes 64. The storage electrodes 62 and plate electrodes 64 can bemade of any conductive or semiconductive material. Typically, thestorage electrodes 62 and the plate electrodes 64 are made ofpolycrystalline or crystalline silicon, a refractory metal such as W,Mo, Ta, Ti or Cr, or suicides thereof such as WSi₂, MoSi₂, TaSi₂ orTiSi₂. Other metals or metal silicides may be used in various designs.It will be appreciated that the electrodes 62 and 64 may be made fromstill other materials without departing from the scope of the invention.In certain embodiments, in the DRAM, the storage electrodes 62 and theplate electrodes 64 of the capacitor 60 are separated by the compositelaminate dielectric layer 12 c that includes the ZrO₂ layer 14 c and thelanthanide oxide layer 16 c.

The capacitor 60 is used to store charge representing one bit of data.Access to the capacitor is made via a wordline 52 and digitline 78. Thewordline 52 is the gate electrode 52 of the transistor 40 that is usedto form a conductive channel between source/drain regions 42 and 44 whensufficient voltage is applied to the wordline 16. In certain embodimentsof the DRAMS of the invention, the gate electrode 52 is located abovethe gate dielectric layer 12 a made of composite laminate gatedielectric material 12, having the ZrO₂ layer 14 a and the lanthanideoxide layer 16 a.

As depicted in FIGS. 4A and 4B, the composite laminate dielectric layer12 is used as both the gate dielectric 12 a as well as the capacitordielectric 12 c. Although depicted for use as both the gate dielectric12 a and the capacitor dielectric 12 c, it will be appreciated that thecomposite laminate dielectric layer 12 may be used in only one of suchlocations, both locations or in other locations in a DRAM where adielectric may be used.

Although the ZrO₂ layer 14 and lanthanide oxide layer 16 in theembodiments shown in the foregoing Figures are depicted with the ZrO₂layer 14 positioned below the lanthanide oxide layer 16, the relativeposition of the layers can be reversed in various applications. Theorder of placement of the layers depends on the particular fabricationprocess for the semiconductor device and relative position of the layerswith respect to other components of the device. In certain embodiments,the ZrO₂ layer 14 can be formed first by depositing the ZrO₂ onto andapproriate surfaces by one of the RS-ALD deposition methods describedherein after. Alternatively, in other embodiments, the lanthanide oxidelayer 16 can be deposited first, using for example, the e-beamdeposition method described herein after. In most embodiments, the ZrO₂layer 14 will be deposited first because the thickness of this layer caneasily be controlled by the number of cycles used in the RS-ALD andtypically forms a smooth surface on polysilicon, crystalline silicon, orother substrates.

Another aspect of the invention includes methods of forming asemiconductor structure that include forming the composite laminatedielectric layer 12 by forming the ZrO₂ layer 14 and then forming thelayer of lanthanide oxide 16 on the surface of the ZrO₂ layer 14, orvice versa.

There are a variety of methods of depositing the ZrO₂ layer used invarious embodiments of the invention. One embodiment uses DCmagnetron-reactive-sputtering from a Zr target in an Ar+O₂ ambientatmosphere with an O₂ flow rate of 2 sccm and total pressure of 40mTorr, as described by for example, by Wen-Jie Qi, et al, TechnicalDigest of IEDM, 145, 1999. The sputtering may be done at differenttemperatures and at different power levels. After sputtering, thesamples are furnace annealed in either an O₂ or an N₂ ambientatmospheres. The ZrO₂ films deposited using this technique are amorphousand form a thin interfacial silicate layer of about 9 Å thickness. Thisinterfacial layer can be minimized through optimization of processparameters such as power and temperature. There is no significantinter-diffusion between ZrO₂ and Si. After high temperature annealing,the layer grows and converts to a more stoichiometric ZrO₂ layer.

Another method for depositing the ZrO₂ layer 14 in certain embodimentsis atomic layer chemical vapor deposition (AL-CVD) as described forexample by M. Copel, et al, Appl. Phys. Lett., 76, 436, 2000. Films ofZrO₂ are grown using alternating surface saturation reactions of ZrCl₄and H₂O at about 300° C. After film growth, the substrates may betransferred in air to a characterization system where they are treatedto in situ annealing under ultra high vacuum or to oxidizing in astainless-steel turbo-pumped side chamber. In certain practices, priorto deposition, a 15 Å thick SiO₂ layer may be grown by thermal oxidationin a separate furnace. In these practices, samples can be treated todilute 5% HF for 2 min prior to AL-CVD growth of the ZrO₂ layer 14 toremove the SiO₂. It should be noted, however, that attempts to grow ZrO₂directly on HF stripped silicon, without prior silicon oxide oxidationmay result in uneven and discontinuous ZrO₂ films.

Another technique for depositing the ZrO₂ layer 14 in certainembodiments, is a pulsed-laser-ablation deposition method as describedfor example, by Yamaguchi et al. Solid State Devices and Materials,228-229, 2000. Ultra-thin ZrO₂ layers having a large dielectric constantand a smooth interface can be formed using this technique.

Another technique for depositing the ZrO₂ layer 14 used in otherembodiments, is in-situ rapid thermal processing as described, forexample, by H. Lee et al, IEDM 2000, 27-30, 2000. Lee et al. reportedthe MOS characteristics of ultra thin, high quality CVD ZrO₂ and Zrsilicate (Zr₂₇Si₁₀O₆₃) gate dielectrics deposited on silicon substratesby this method. These high-k gate dielectrics showed an excellent EOT of8.9 Å (ZrO₂) and 9.6 Å (Zr₂₇Si₁₀O₆₃) with extremely low leakage currentof 20 mA/cm² and 23 mA/cm² at Vg=−1 V, respectively.

Yet another method for depositing the ZrO₂ layer 14 in otherembodiments, is Jet-Vapor-Deposition (JVD), as described, for example,by Z. J. Luo et al., 2001 Symposium on VLSI Technology Digest ofTechnical Papers, 135-13 Luo et al. demonstrated that films with EOT of1 nm possess high thermal stability, low leakage, high reliability andother good electrical properties. The composition of JVD films varieswith thickness. Thinner films are found to be Zr silicate-like whereasthicker films are likely graded with a transition to stoichiometricZrO₂. In addition, these films were found to survive annealingtemperatures as high as 1000° C.

Still another method for forming a ZrO₂ layer 14 in other embodiments,is to use a modification of the low temperature oxidation method forforming a silicon oxide layer described, for example, by Saito et al.which uses oxygen generated in a high-density krypton plasma (ExtendedAbstracts of the 1999 International Conference on Solid State Devicesand Materials”, 152-153, 1999. In the modified method, instead ofoxidizing silicon with atomic oxygen generated in the high-frequencykrypton plasma at about 400° C., a thin film of Zr is first deposited onthe silicon substrate by simple thermal evaporation, preferably usingelectron-beam evaporation of an ultra high purity Zr metal slug at a lowtemperature of about 150-200° C. This forms a thin film of Zr on thesilicon while maintaining an atomically smooth surface. After formingthe layer of Zr metal, it is oxidized to ZrO₂ using the high frequencykrypton plasma at about 300-500° C.

Still another and more preferred method for forming the ZrO₂ layer 14 inother embodiments, is to use reaction sequence atomic layer deposition(RS-ALD) of a ZrI₄ precursor followed by deposition of oxygen reactantsin multiple cycles to sequentially grow the ZrO₂ layer as described, forexample, by Kukli et al., J. of the Electochemical Soc., 148 (12)F227-F232, 2001. In this method, the silicon substrate is first etchedby treatment with about 5% HF to remove any native SiO₂ formed on thesurface. The etched substrate is then placed in an RS-ALD reactionvessel along with an open reservoir containing the ZrI₄ precursor. Thepressure in the reaction ALD reaction vessel is lowered to a value ofabout 250 Pa or lower for one or more pulse periods of about 0.5 to 5seconds. A pressure of about 250 Pa is a suitable pressure forevaporating the ZrI₄ and a pulse of about 0.5-2 seconds is sufficient todeposit a layer of about 0.5 to 5 angstroms per cycle. The temperaturein the reaction vessel is typically maintained between about 230 and325° C. Oxygen is then supplied by a vapor of an H₂O—H₂O₂ precursorgenerated form an external reservoir at room temperature. The oxygenprecursor material is passed into the ALD reaction vessel after eachZrI₄ evaporative precursor pulse for a period of about 2 seconds orless.

Between each ZrI₄ evaporation pulse and oxygen pulse and between eachoxygen pulse and the next evaporative pulse, the reaction vessel ispurged with a suitable carrier gas, such as nitrogen or a noble gas, toseparate the precursors flows in the gas phase and remove excessreactants and by-products from the system. A suitable purge time forefficiency is about 2 seconds or less. Approximately 6 to 50, andtypically about 10-20 evaporative cycles of 2 seconds in duration at atemperature of about 230 to 600° C. is suitable for forming a ZrO₂ oxidelayer of about to 2 to about 5 nm in thickness. In various embodiments,temperatures of about 230° C. to 350° C., 272-325° C. or 272-275° C. areused because less residual iodine remains in the final layers and thesetemperatures lead to better quality oxides having a cubic ZrO₂ latticestructure at the silicon/ZrO2 interface only giving way to a tetragonallattice structure with increasing layer thickness. Temperatures greaterthan about 350° C. tend to form films with more t-ZrO₂ structure andreduced capacitance. The permittivity of a ZrO₂ layer of 2 to 5 nm inthickness made the foregoing method is about 2-8 at 100 kHz and has anEOT of about 0.3 to about 2.4 nm.

Once the ZrO₂ layer 14 is deposited, the lanthanide oxide layer 16 isdeposited thereon by any suitable technique. A preferred technique fordepositing the lanthanide oxide layer is e-beam evaporation. FIG. 5illustrates an e-beam evaporator chamber 90 suitable for forming thelanthanide oxide layer 16 (or in certain embodiments, for forming a Zrprecursor layer) according to the invention. The e-beam evaporatorincludes a removable chamber vessel 92 made of metal, quartz or othersuitable high temperature tolerant material. The chamber vessel islocated on top of a base plate 94. The substrate 96, optionally with apreviously deposited layer of ZrO₂ 14, is held in a substrate supportdevice 98 with the target surface facing a shutter 100 that controlsexposure of the substrate surface to the beam of evaporated lanthanideoxide 102 emitted by bombardment from an electron gun 104 situated inthe lower part of the chamber below the shutter 100.

The temperature of the substrate 96 and chamber environment iscontrolled by a heater 106 assembly that may include an optionalreflector 97 in proximity to the substrate 96. The temperature in thechamber is raised to about 2000° C. to ensure efficient e-beamevaporation and deposition of the lanthanide oxide 102. An oxygendistribution ring 108 is located below the shutter 100. The oxygendistribution ring is a manifold that distributes oxygen around thesurface of the substrate 96 at final pressure of about 10⁻⁷ Torr. Theelectron beam evaporation chamber 90 is configured with a vacuum pump110 for evacuating the chamber to a pressure of about 10⁻⁶ Torr or less.Oxygen pressure in the chamber is regulated by oxygen control regulator112. A small amount of oxygen is needed in the chamber to ensure thatthe deposited layer of lanthanide oxide is completely oxidized becausethe process of e-beam evaporation tends to degrade the oxidationstoichiometry of the lanthanide oxide material 102. Optional detectorsor monitors may be included on the interior or exterior of the chamber90, such as an interiorly situated detector 114 for detecting thethickness of the layer and the exteriorly situated monitor 116 fordisplaying the thickness of the layer. The lanthanide oxide layer 16 isformed to a suitable thickness of 2-10 nm on the surface of thesubstrate or ZrO₂ layer 14 by controlling the duration of electron beamevaporation.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the following claims.

1-41. (canceled)
 42. A method of forming a composite laminate dielectriclayer for a semiconductor structure, comprising forming a first layer ofa material selected from the group consisting of ZrO₂ and lanthanideoxide on a substrate; and forming a second layer of material selectedfrom the group consisting of ZrO₂ and a lanthanide oxide on the firstlayer of material, the second layer of material being different from thefirst layer of material.
 43. The method of claim 42 wherein the firstlayer of material is ZrO₂ and the second layer of material is thelanthanide oxide.
 44. The method of claim 42 wherein the first layer ofmaterial is the lanthanide oxide and the second layer of material isZrO₂.
 45. The method of claim 42 wherein the lanthanide oxide isselected from the group consisting of Pr₂O₃, Nd₂O₃, Sm₂O₃, Gd₂O₃, Dy₂O₃and PrTixOy.
 46. The method of claim 42 wherein depositing the ZrO₂ isperformed at a temperature of about 230-325° C.
 47. The method of claim42 wherein the act of depositing the ZrO₂ oxide includes atomic layerdeposition of a ZrI₄ precursor followed by oxidation with H₂0/H₂O₂. 48.The method of claim 47 wherein the atomic layer deposition is performedat a temperature of about 230-325° C.
 49. The method of claim 47 whereinthe atomic layer deposition is performed at a temperature of about272-275° C.
 50. The method of claim 42 wherein the lanthanide oxidelayer is formed by electron beam evaporation of the lanthanide oxide.51. The method of claim 42 wherein the ZrO₂ oxide layer is formed byatomic layer deposition of a ZrI₄ precursor followed by oxidation withH₂0/H₂O₂ and the lanthanide oxide layer is formed by electron beamevaporation of the lanthanide oxide.
 52. The method of claim 42 whereinthe ZrO₂ layer is formed to a thickness of about 2-5 nm.
 53. The methodof claim 42 wherein the lanthanide oxide layer is formed to a thicknessof about 2-10 nm.
 54. The method of claim 42 wherein the ZrO₂ layer isformed to a thickness of about 2-5 nm and the lanthanide oxide layer isformed to a thickness of about 2-10 nm.